1. Field of the Invention
The present invention relates to a white balance adjusting apparatus for accurately displaying a luminance signal on a television receiver or a computer display unit using a cathode ray tube and, more particularly, relates to a white balance adjusting apparatus which is suitable for being formed in an integrated-circuit and can easily adjust the white balance in a manufacturing line.
2. Description of the Related Art
The television receivers and computer display units are subjected to the white balance adjustment in the manufacturing line thereof. The white balance adjustment methods include the cut-off adjustment for adjusting the balance among red, green and blue (RGB) at faintly brightening dark level (black signal) and the drive adjustment for adjusting the balance among red, green and blue at strongly brightening brightness level (white signal).
The cut-off adjustment means the adjustment of DC levels (biases) of RGB output signals, while the drive adjustment means the adjustment of AC levels (gains) of RGB output signals.
A method for adjusting the white balance in a simple manner has been considered. For example, each of the red, green and blue may be adjusted in a manner that each color is brightened independently, then a beam current (IK) of the brightened beam of the color is detected and then adjustment of the color is performed. The beam current (IK) represents the cathode current of each of the primary colors of the red, green and blue.
The method for adjusting the white balance in a simple manner also performs the cut-off adjustment and the drive adjustment. An amount of the beam current (IK) largely differs between the cut-off adjustment and the drive adjustment. For example, the beam current flowing at the time of the cut-off adjustment is 25 microampere, whilst the beam current flowing at the time of the drive adjustment is about 3.5 milli-ampere.
Thus, a dedicated input circuit and a dedicated discrimination circuit are required for each of the cut-off adjustment and the drive adjustment.
However, in this case, there arises a problem that the requirement of the dedicated input and discrimination circuits for each of the cut-off adjustment and the drive adjustment results in the increase of the number of elements of the adjusting apparatus.
Further, the input circuit is formed by a discrete element disposed at the outside of an integrated circuit (IC) in order to obtain a resistance value with a high accuracy. Thus, there also arises a problem that the IC requires another pin for applying a signal to the discrimination circuit disposed within the IC and so two pins in total are required for the cut-off adjustment and the drive adjustment.
Furthermore, there is a problem that it is troublesome to adjust the white balance in the manufacturing line. That is, conventionally, a measuring and adjusting computer is disposed in the manufacturing line and the wiring and adjusting operation is performed for each IC conveyed along the manufacturing line.
Further, since the white and black signals are required to be supplied to the IC at the time of adjusting the white balance, conventionally it is required to dispose a test signal generating apparatus at the manufacturing line so that the white and black signals are supplied to the IC from the outside. Thus, an amount of work at the manufacturing line increases and so the white balance adjustment is more troublesome.
The present invention has been performed in order to solve the aforesaid problems and an object of the present invention is to provide a white balance adjusting apparatus which can easily perform the cut-off adjustment and the drive adjustment in the manufacturing line.
A white balance adjusting apparatus according to a first aspect of the present invention is a white balance adjusting apparatus for performing cut-off adjustment and drive adjustment for each of primary color signals of red, green and blue, comprising:
three DC adjusting circuits for adjusting DC levels of the primary color signals of red, green, blue and three AC adjusting circuits for adjusting AC levels of the primary color signals of red, green, blue, respectively;
three drive transistors for amplifying the primary color signals of red, green, blue, respectively and driving an image display unit;
a variable impedance means coupled to the three drive transistors and arranged to have at least two resistance values;
a switch means for switching the resistance value of the variable impedance means;
a reference voltage source for generating a first reference voltage at a time of performing the cut-off adjustment and generating a second reference voltage at a time of performing the drive adjustment;
a comparator for comparing levels between the reference voltage of the reference voltage source and a terminal voltage of the variable impedance means; and
a control circuit for generating a control signal for adjusting white balance on a basis of an output signal of the comparator and adjusting DC levels and AC levels of the primary color signals of red, green, blue by using the DC adjusting circuits and the AC adjusting circuits.
According to such an arrangement, both the cut-off adjustment and the drive adjustment, wherein used signal levels differ extremely therebetween, can be processed with a single input circuit and a single discrimination circuit, so that the number of the circuit elements can be reduced.
According to a second aspect of the present invention, the white balance adjusting apparatus according to the first aspect further comprising a test signal source for generating a signal for the drive adjustment and a signal for the cut-off adjustment.
According to such an arrangement, a signal source in a test line can be eliminated.
According to a third aspect of the present invention, the white balance adjusting apparatus according to the first aspect is arranged in a manner that an output value of the reference voltage source is arranged to change interlockingly with an output value of a reference voltage source of a clamp circuit for setting the levels of the video signal to a constant level.
According to such an arrangement, when the output value of the reference voltage source of the clamp circuit changes, the output value of the reference voltage source changes interlockingly therewith, so that the accurate signal for testing can be obtained.
According to a fourth aspect of the present invention, the white balance adjusting apparatus according to the third aspect is arranged in a manner that the variable impedance means includes a first resistor and a second resistance element connected in parallel with the first resistor and having a resistance value smaller than that of the first resistor, and the switch means is a switch for selectively connecting and disconnecting the second resistor to and from the first resistance element.
According to such an arrangement, the output signal level of the variable impedance means can be easily adjusted for the cut-off adjustment and the drive adjustment by merely switching the switch.
According to a fifth aspect of the present invention, the white balance adjusting apparatus according to the second aspect is arranged in a manner that the resistor is a discrete element disposed at an outside.
According to such an arrangement, since the second resistance element is disposed at the outside, it is not necessary to adjust the output value of the reference voltage sources. Further, according to such an arrangement, since it is not necessary to adjust the reference voltage sources, the reference voltage sources can be disposed within an IC.
According to a sixth aspect of the present invention, the white balance adjusting apparatus according to the second aspect is arranged in a manner that the DC adjusting circuits, the AC adjusting circuits, the comparator, the control circuit and the test signal source are integrally formed on a single substrate.
According to such an arrangement, the number of the pins can be reduced and the size of the apparatus can be miniaturized.
According to a seventh aspect of the present invention, the white balance adjusting apparatus according to the second aspect is arranged in a manner that the test signal source is disposed at a circuit disposed outside.
According to an eighth aspect of the present invention, the white balance adjusting apparatus according to the first aspect is arranged in a manner that the control circuit is a circuit disposed outside.
According to such an arrangement, the adjustment of the control circuit can be performed easily.
According to a ninth aspect of the present invention, the white balance adjusting apparatus according to the first aspect is arranged in a manner that the DC adjusting circuits, the AC adjusting circuits and the drive transistor circuits for the primary color signals of red, green, blue are operated in time sequence so that the cut-off adjustment and the drive adjustment for the primary color signals of red, green, blue are performed in time sequence.
According to such an arrangement, since the adjustment can be performed by a single variable impedance means and a single comparator, the number of the circuit elements can be reduced as compared with the case where the adjustments are performed simultaneously.
According to a tenth aspect of the present invention, the white balance adjusting apparatus according to the first aspect is arranged in a manner that the control circuit includes a latch circuit for latching three discrimination outputs for the primary colors of red, green, blue from the comparator, a timing controller for controlling latching timing of the latch circuit, and a microcomputer for generating the control signal for adjusting the white balance on a basis of an output of the latch circuit.
According to such an arrangement, since an automatic adjusting loop for adjusting the white balance can be formed, a computer for measurement and adjustment in a manufacturing line can be eliminated.